7 free services for checking sites (which you might not know)

I often have to use various online services to check the availability of sites and their surface tests and checks.
As shown by a brief survey of colleagues - almost all of these sets of services are different. I want to show you my, please in .

LoadImpact: http://loadimpact.com , service load testing sites (for money - up to 5k simultaneous connections) which has a free test for 50 simultaneous connections. If you are hosted by the ruthless and merciless domestic host for $ 0.01 / month and you have only a thousand sites on the server - try to test your own, with high probability it will not even endure 50 simultaneous connections.

BrowserMob: http://browsermob.com , an additional simple but nice service that allows you to check the download speed of the target site from 4 different places and showing many detailed download metrics for each of them. And the main task of BrowserMob is automatic cross-browser testing of sites.
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Alertra: http://alertra.com , uptime monitoring service, on the site of which you can check the availability (and response time) of the site from 11 different places for free. It works quickly and reliably, no caps and other rubbish.

site24x7: http://site24x7.com , similar to the Alertra service, which already uses 23 geographically distributed verification points.

You get signal: http://www.yougetsignal.com , an excellent service that allows you to check open ports on any host / IP. It often helps to check port forwarding through NATs.

Now let's move on from accessibility checks to slightly more complicated things. I will not write about w3c-shnye products, I hope everyone already knows and uses them.

CSE HTML Validator: http://www.onlinewebcheck.com is an alternative to the well-known validator.w3.org , built [apparently] on its own separate analysis core. Favorably differs very detailed and understandable recommendations for correcting errors and potential problems.

Built with: http://builtwith.com/ analyzes the given site and gives out a whole dossier about it: a web server, a CMS, which statistics service is used, and so on. There are a lot of indicators, for a quick analysis of competitors is quite suitable. Also, it is interesting to delve into the trends.builtwith.com where the owners of the service give statistics on all monitored parameters. For example, the vast majority of sites still use the old blocking JS-code for Google Analytics.

And what services do you have in bookmarks?